1. Field of the Invention
The invention relates generally to the suppression interference amongst communication signals. More particularly, the invention relates to the implementation of statistical techniques to interference suppression.
2. Description of the Related Art
Radios may receive three forms of signals: noise, interference and communication. Noise, created in the atmosphere due to natural causes such as lightning and the like, is unpredictable. Few steps are taken towards elimination. Interference signals can be caused such as by several stations broadcasting on the same band, or can be caused deliberately, such as by an adversary transmitting signals to mask communication signals. Many techniques have been devised to combat interfering signals.
As major sources of radio interference are non-Gaussian in structure, one such technique for detecting communication signals in the presence of non-Gaussian interference has been known to employ algorithms that estimate the statistics of this interference. This estimate is then used to transform received radio signals into perceptible communication signals.
One statistical technique creates a probability density function (PDF) from discrete data. This method creates a transform for continuous data based upon the derivative of the natural log of the PDF of a magnitude, such as signal amplitude. Researchers have estimated the PDF of signal amplitudes of interfering signals by creating histograms of received data. These researchers then used finite difference operations to estimate required derivatives.
The histogram approach is known to be numerically unstable and, to be satisfactory, requires that a relatively great number of signal samples be taken. This high sample requirement makes the histogram approach computationally demanding and confines its use mainly to dedicated microprocessors, and then for those used with radios operating in the lower portion of the radio frequency spectrum (low frequency (LF), very low frequency (VLF) and extra low frequency (ELF)). In higher frequency ranges, sufficient sampling becomes extremely difficult.
In environments in which interference characteristics are radically and rapidly changing, the necessity to collect a large number of samples over time makes alternative approaches to the histogram technique worth investigating.
There is thus a need for an interference suppression system that can be used with dedicated or nondedicated microprocessors, that is suitable for use with radio receivers operating over both the lower and upper portions of the radio frequency spectrum and that can provide satisfactory interference suppression in radically and rapidly changing interference environments.